1. Field of the Invention
This invention relates to an implantable electrode lead to be used in conjunction with such an implanted device as a cardiac pacemaker and a defibrillator. More particularly, it relates to a structure of an implantable electrode lead having improved operational efficiency during the course of being implanted in vivo or ligated to a vital tissue by providing at specific portions thereof with a lubricating coat layer.
2. Description of the Related Art
Numerous kinds of implantable electrode leads for the use in conjunction with such an implanted device as a cardiac pacemaker and a defibrillator have been known to the art.
The cardiac pacemaker is a device for electrically stimulating a heart directly thereby increasing a heart rate. There are two types of cardiac pacemakers, namely an external cardiac pacemaker which is disposed outside a patient body and an electrode thereof is introduced into the heart of the patient and an implanted cardiac pacemaker which itself is present in a patient body. Without reference to this classification, the cardiac pacemaker requires an implanted electrode lead to be retained in a heart or intravenously for the purpose of transmitting the electric stimulation from the cardiac pacemaker to the patient body. Thus, the implanted electrode lead is generally composed of (i) at least one electrode adapted to impart electric stimulation to a heart or detect an electric excitation of a heart, (ii) a connecting means for electrically connecting to such an implanted device as a cardiac pacemaker and a defibrillator, and (iii) a conducting part consisting of an electric conductor and an insulating coating for covering the outside of the electric conductor.
Incidentally, an implantable electrode lead to be used intravenously has a structure such that an electrode and part of a conducting part are introduced into a heart or intravenously and the conducting part and a connecting means remaining outside the vein are connected to an implanted device such as a cardiac pacemaker and a defibrillator.
A conventional implantable electrode lead in a implanted state will be described below by reference to FIG. 1. A whole length of an implantable electrode lead extends from a “proximal end” in the neighborhood of a cardiac pacemaker 10 to a “distal end” located farthest from the cardiac pacemaker 10. The proximal end comprises a connecting means for connection to the cardiac pacemaker 10 and the distal end comprises a tip electrode 40, a ring electrode 42, and the like as endocardiac electrodes besides an endocardium-fixing means 50 to be fixed to a vital tissue. A conducting part 30 which extends from the proximal end to the distal end is provided with a suturing sleeve 60 which is capable of being moved along the outer surface of the conducting part 30. For the fitting thereof, the distal end of the implantable electrode lead is introduced via a subclavian vein into a heart chamber, implanting the distal end of the lead at a proper site in the heart chamber, and fixing the tip electrode 40 and the ring electrode 42 in the heart chamber as with the endocardium-fixing means 50 or a screw for ensuring the retention at that site. Generally, at a site of the lead inserted intravenously and at a further proximal site thereof, the suturing sleeve 60 is ligated on the outer periphery thereof with a suture to fasten the conducting part 30 and the vital tissue in order to prevent the migration or elimination of the electrode.
When both the atrium and ventricle of a heart are required to be stimulated at the fitting of the implanted electrode lead, it becomes necessary to have two leads, i.e., a lead 31 for the ventricle and a lead 33 for the atrium, implanted. When these two leads are to be introduced into a small blood vessel or a tortuous blood vessel, they possibly interfere with each other to an extent of rendering the introduction difficult and they have even a possibility that the formerly implanted lead will be moved out of position by the subsequently implanted lead. This phenomenon is conspicuously observed particularly in leads which use a silicone sheath. Thus, a technique for ensuring satisfactory efficiency for the implanting work by subjecting to the surface of a conducting part such a treatment as decreasing the friction thereof has been developed. JP-A-08-10338, for example, discloses an electrode lead for the use in a cardiac pacemaker which comprises a tip electrode part, a connecting means and a conducting part having a surface coated with a hydrophilic polymer and consequently endowed with improved lubricity.
When the lubricity of the surface of the conducting part is improved by coating the surface with a hydrophilic polymer as described in JP-A-08-10338, however, although the introduction of the lead during the implantation process can be easily attained, the subsequent ligation of the lead to a vital tissue by means of a suturing sleeve entails a possibility that the suturing sleeve would slip on the conducting part to degrade the fastness of the ligation and thus the lead could not stably fixed in a body. As a result, there is also a possibility that the electrode would be randomly moved or even slipped out to render the pacing and the sensing imperfect. This adverse effect results in harming the performance which the implanted device such as a cardiac pacemaker or a defibrillator ought to manifest inherently.
This invention is directed toward realizing an implantable electrode lead which can manifest lubricity enough to introduce the implantable electrode lead and be fixed for a long time even in the case of the ligation of the lead to a vital tissue, and thus permits the stable transmission of an electric signal from the implanted device to the vital system.